In this time when progressing an earth warming, in order to make a woody pellet fuel from Ogako, the moisture content of Ogako affects the quality of the product of which, therefore the drying of Ogako is important process. However, a lot of thermal energy is necessary to dry the Ogako, and fossil oil has to be greatly consumed as energy source. From a view point of energy saving and fossil oil free techniques, all weather passive-type solar Ogako drying method is seriously effective and useful.
Two types of Ogako dryer are known.
1) Rotary kiln-type Ogako dryer which is a well known batch system, peculiarities of which are as follows:
a. an expensive facility,
b. being fire dangerous under bridge flame (high temperature),
c. too much consumption of fuel and electric power,
d. to be suitable for large scale facility, but
e. uniform quality of the production.
2) Air absorption-type Ogako dryer which is another well known batch system, peculiarities of which are as follows:
a. an expensive facility,
b. yielding of Ogako dust,
c. too much consumption of fuel and electric power,
d. to be suitable for large scale facility, but
e. uniform quality of the production.
3) Some solar dryer by which high moisture substances such as sullage and bean-curd refuse can be dried cheaply by evaporation due to solar thermal energy and so as out of auxiliary heat, and dehydration due to capillarity phenomena of fibrous belt of the conveyor has been known (Japanese Published Unexamined Patent Application No. 05-185098).